Controlling alkalinity of drilling fluids



Patented July 15, 1 952 CONTROLLING ALKALINITY OF DRILLING FLUIDS; 3

- Victor G; Meadors, Tulsa,-..0kla.,1iassignor to i Standard Oil Development com anl' acorporation of Delaware No Drawing. Application April 1, 1950,

Serial No. 153,490 7 Claims. (01. ase -8.5)

The present invention relates to the treatment of drilling muds employed in the drilling of oil and gas wells. More specifically it concerns the use of particular addition agents for controlling the alkalinity of aqueous drilling V muds.

In the drilling of oil and gas wells, particularly with rotary drilling apparatus, it is common practice to circulate around the drill in bore hole a fluid known as a drilling mud which serves a number of functions, including carrying the bit cuttings out of the bore hole, lubricating the drill pipe and drilling tool, and providing a hydrostatic head in the well to prevent the uncontrolled escape of gases or liquids from various formations encountered during drilling. The drilling mud also serves to form a lining on the wall of the bore hole which helps t'oprevent the walls of the bore hole from caving and to plug up'permeable formations and thereby prevent the flow'of'fiuid from the' well bore outwardly into the permeable formations. The normal procedure during drilling is to circulate the mud downthrough the interior of the drill pipe and then' back up to the surface through the annulus between the drill pipe and the wall of the borehole. The drilling mud issuing from the well is usually passed'over a'screen and thenthrough' a ditch or trough to a mud pit, to be recirculated through the drill pipe by suitable pumps. 7 r

The most common type of drilling mud is essentially a dispersion of a finely divided colloidal material, such as clay, bentonite or the like, in water; together with other materials so that the mud will have the special properties required to perform the several functions enumerated above. Among the properties of the mud-that are of principal concern are viscosity, gel strength, and density. The proper density is necessary to furnish sufficient hydrostatic head in the borehole sothat the pressure exerted will exceed that of the various fluids encountered in the formations traversed by the borehole. Weighting materials such as silica, iron oxide or barytes, more commonly the latter, are usually added to the drilling mud to provide the proper density. Viscosity and gel strength are imparted by the clay or bentonite component. A typical drilling mud will have a'density of from 9 to I 18 poundsitpergallon and in general, forJsatisfactory drillingwill have aiviscosityof about to centipoises at 75 F. as measured on the Stormer viscosimeter at 600 R. P.v M., although in, some deep drilling operations viscosities as high as 60 centipoises; may be employed. p

, It; is important that a drilling mud have thixotropic properties, i. e. itshould be fluid when'subjected to, agitation but when standing should setto a gel of sufficient strength to retain cuttings in the time required for the cut tings to settle a few, feet. In order to perform the function of carrying cuttings from the drill bit to the ,earths surface where the cuttings drop out in the mud pit, the drilling fluidmust have a selected viscosity such that the fluid may be pumped through the system, and also such that the cuttings will remain suspended inthe fluid during the flow of the fluid up the bore hole Also the fluid, when it is relatively quiescent, should permit the cuttings to fall a few feet since it isessential that thecuttings settle out at the-surface; On the other hand, .the fluid should-have the property of gelling von standing, in order to prevent undue settling of the cuttings in the well itself when-drilling and circulation of fluid are temporarilyhalted.

Another important property of a drilling mud that must be controlled iswhat is :known as its fluid loss, oryflltration loss, characteristics. .Because of differences in hydrostatic pressure between the drilling mud and the formation being drilled there is a-tendency for the liquid component of the mud to enter into the pores of the formation, leaving a solid component behind as a cake on the walls of the bore hole. If

the permeability" of the formation and the fluid loss properties of the drilling mud are both high, large quantities of the liquid component may be lost from the mud, resulting in the building up of a wall-cake which in some instances may become so thick as to interfere seriously with movement of the drill pipe even to the extent ,of'cau'sing the pipe to stick in the hole. Furthermore," if a thick cake is formed over the face of' a producing formatiomthere is danger that it-will not be properly cleaned off during the process of completing the well, with the result that the production rate of the well will be seriously impaired. :In addition, with high strength and fluid loss properties can be pre pared by dispersing the proper amount, of -bentonite in water. However, when certain salts, particularly those of calcium and magnesium, become dissolved or dispersed insuch a-drillingmud during use as the result of havingencountered strata containing these salts during 4 from about 0.1% to about 10%, and preferably in amounts of about 0.1% to about 5%.

Although other amino compounds will efiectively raise the pH of an aqueous drilling mud their use is undesirable because of their tendency to increase the viscosity of the drilling mud to more than a moderate degree. Comparison of the alkanolamines of this invention with other amino compounds in a drilling mud composition was made by means of the following tests. An aqueous slurry containing 4% of? bentonite was prepared and was found to have a viscosity of about 5 centipoises at 75 F. as measured by the Stormer viscosimeter at 600 R. P. M. Various concentra tions of alkanolamines and of other I amino compounds were added to portions of this slurry and the effect on viscosity and pH was drilling, the fluid loss propertiesofthe drilling hmud are adversely affected. To overcome-.this. it is now frequent practice to add to the drilling V mud certain organic materials such as corn-- starch, wheat flour, gum tragacanth, locust bean gum, gum arabic and :the like. The: use or starches and-gums in drilling muds has a. disv advantage in that such materials-tend to undergo fermentation or bacterial decomposition. Inorder to prevent such-fermentation, as well: as to enhance 'thepromotion of I low. fluid loss-prop erties when using-gums or starches it has been found advisable tdmaintainthe pHIof: the drilling mud at least: above and preferably above 11' or 11.5.- This-is usually accomplishedf'by: adding causticsoda to the-mud.- However, it

frequently happens that when this-is done anundue increase in viscosity. of the mud: occurs and this must be corrected byadding a: viscosity. controlling agent such asquebracho. Insome instances itis not possibleto. control. the viscosity even with such additives:anditqisethen' necessary-to thin: the mudv addingwater; which: in turn impairs the. gel strength: of ;.the; mud. This. calls forfurther treatment;..of. the. mud-withzother addition agents.: j lthasrthuselong been.apparentzthatathere is;

need fora-materialwhich .canzbeaddedto a.dri l1-:

lng mud: to raise; its:- .pl-Ii value- ,wjithcmt at, the same. time adversely: aliectingg its vis cosity;.-l It has now. been found; in; accordance Withn the, present invntidm. thatralkanolam nfi r. narticu'e larly the Zethanolamines, .will iefiiect-ively; raisethe pH of :an ;aqueo.us drilling. mud: to. its desirecl; value of;r1;or;mo.re,wi.th ut mat r a e n reasing the viscosity .of the m-ud-u [Ijhe,.alkano 1amines. that; are; 1 5. 5 1l in th-i inventio are thosehavinaaztotalpf not more;than;15zcarbon atoms. and- ;havin g,not more than 3. -ca.rbon atomsbe tween zthei-hydroxylg group and the amino group. in thealkanol' radi a I It; is-believed; that; this proximity of. the.-

hydroxyl and: amine roups; exerts. a stabilizing;- effectwhichenables the attainment o thedesired pH.without..causingfidccl letifin Qfithebentonite' 0r otherclay-used-in t ezdri i gim i: 1 intendedzhowevelf thatcthe inv ntion be l mit by;an-y theoryasgtoits modeof operation. I The alka'nolamines:thateare:particularly-me; ferred; are monoethanolamine.., diethanolamine a d; triethanolan iinew; Qther; members. of. this. class. that: may; be employed include propanoleamine, dimethylethanohiamine-,zand fli ihylethr anolamine. In general .theseralkanolamineswill.

be added-to thedrilling-muddh: amounts ranging 75 measured; thep H-vvalue being obtained with a Beckman. pH meter, and the viscosity with a Storlner'viscosimeter. The results obtained are giveninzthe following table.

Percent Percent Amme y Increase in pH Weight Viscosity Ethanolaminm Dimethylethanolamine; 8'? 8 Diethanolamine 3 5g 3 0.3 11.0 Triethanolamme 0.8 p 11.0 u 1.5 40 11.0- Diet'hylaminelflun 0.3. 720 1213. ne e It will. be seen that :althoughthe alkanolamines causedonlya slight increase iii-viscosity; diethyl about-.0:8 of neamyl amine brought about a980- percentincrease; and; additionof about 0.5% ofdimethyl; amine caused .a 500 percent increase; in-

c si y- Althoughmaintenance of a high pHin'drilling muds is; of particular benefit for preventing fer-- mentation of starch or. gums, it is also often desirable-to maintain ahigh pH to prevent corrosionofdrilling'equipment. Hence the benefits of: this-invention extendto all, aqueous drilling muds that wouldordinarily. tend to become unduly thickened when attempting to maintaina high. pH by adding sodium hydroxide or other strong; alkalies thereto.

It is; intended that this invention. be limited only by theappge dedrclaims and not by the fore-- going; specific examples.-

- What-.is.claimed.is':

;.1'. A-- ,dril-l ing-fluid-comprising an aqueoussus-- pension'of-a clay to. which has been added sufii.--

cientzalkanolamine to raise-the pI-I ofthe-com positionto at; least. 10, saidalkanolamine being characterized having; a .total. of .not' more-than" l5 carbonatoms and notmore 3 carbon atomsv between the-hydroxyl group and the-aminoqgroup in; the alkanol. radical.

' 2..Adrilling, fluidaccording to claim 1.in which.

the: alkanolamineris added in--the' amount of :from about, 0.11% 430.43.10011171 10%.

Aidrillin r fillidaccording-zto. .claiml in which:

the ealkanolaminezisselectedjrom .the class 0011! sisting of monoethanolamine, diethanolamine and triethanolamine.

4. A drilling fluid comprising an aqueous suspension of bentonite and from about 0.1 to about 10% of monoethanolamine.

5. Adrilling fluid comprising an aqueous suspension of bentonite and from about 0.1 to about 10% of diethanolarnine.

6. A drilling fluid comprising an aqueous suspension of bentonite and from about 0.1 to about 10% 01' triethanolamine.

'7. A drilling fluid comprising an aqueous suspension of bentonite and from about 0.1 to about 10% of dimethyl ethanolamine.

VICTOR G. MEADORS.

REFERENCES CITED The following references are of record in the file of this patent: I

UNITED STATES PATENTS OTHER REFERENCES Synthetic Organic Chemicals, Carbide and Carbon Chem. Corp., 1945, p. 7'7. 

1. A DRILLING FLUID COMPRISING AN AQUEOUS SUSPENSION OF A CLAY TO WHICH HAS BEEN ADDED SUFFICIENT ALKANOLAMINE TO RAISE THE PH OF THE COMPOSITION TO AT LEAST 10, SAID ALKANOLAMINE BEING CHARACTERIZED BY HAVING A TOTAL OF NOT MORE THAN 15 CARBON ATOMS AND NOT MORE THAN 3 CARBON ATOMS BETWEEN THE HYDROXYL GROUP AND THE AMINO GROUP IN THE ALKANOL RADICAL. 